Wind energy conversion apparatus

ABSTRACT

A wind energy conversion apparatus comprising a supporting structure including a number of spokes, which is rotatably journalled on a horizontal main shaft, wherein auxilliary rotors having an at least substantially circular plane of inflow are mounted on the ends of the spokes, wherein each of the auxilliary rotors has a plane of inflow which includes an acute angle with the central axis of the main shaft and which intersects the central axis upstream of the main shaft, and wherein the auxilliary rotors are made up of rotors including rotor blades or of conical bodies having a large apex angle, whose base is directed towards the oncoming wind.

The invention relates to a wind energy conversion apparatus comprising asupporting structure including a number of spokes, which is rotatablyjournalled on a horizontal main shaft, wherein wind capturing meanshaving an at least substantially circular plane of inflow are mounted onthe ends of said spokes.

Wind energy conversion apparatuses of the kind referred to above havebeen known for quite some time already in the form of the well-knownwindmills and wind turbines. The wind capturing means that are usedthereby are usually in the form of wings or rotor blades, which arerotatable about a horizontal main shaft. The horizontal main shaftthereby extends in the direction of the oncoming wind, all this in sucha manner that the plane of inflow of said wind capturing means extendssubstantially perpendicularly to the main shaft and also substantiallyperpendicularly to the direction of the oncoming wind.

For a long time already people have attempted to convert an increasingamount of wind energy into other forms of energy. It is known that thiscan be achieved by enlarging the area that is covered by the windcapturing means. This can be accomplished by using wings or turbineblades having a greater length. The large mechanical forces that act onsuch long wings or turbine blades place limitations on said length,however.

Another way of enlarging the area covered by the wind capturing means isknown from WO 96/00349, FIGS. 10 and 11. Said document discloses a windturbine comprising a supporting structure (main rotor) including spokes,which is rotatable about a horizontal main shaft and wherein auxiliaryrotors are disposed on the ends of said spokes. Said auxiliary rotors,which function as wind capturing means, are thereby so positioned thattheir plane of inflow extends perpendicularly to the main shaft. A largearea is covered with this construction, whilst the length of the rotorblades can be relatively small, so that the mechanical forces that areexerted on said blades can be kept within bounds, especially when, as isalso shown, the main rotor and the auxiliary rotors are rotated inopposite directions. The wind capturing means, in this case theauxiliary rotors, of said prior art turbine cover a very large area, asa result of which a large amount of energy is extracted from theoncoming air.

The object of the invention is to improve the aforesaid prior artapparatus and to provide a wind energy conversion apparatus which, giventhe same dimensions and the same wind conditions, is capable ofconverting a larger amount of wind energy into other forms of energy.

In order to accomplish that objective the wind energy conversionapparatus according to the invention is characterized in that each ofsaid wind capturing means has a plane of inflow which includes an acuteangle with the central axis of the main shaft and which intersects saidmain shaft upstream.

Surprisingly, said inclined position of the wind capturing means, which,as will be explained in more detail yet, may be made up of rotorsincluding rotor blades, which are disposed on the spokes of thesupporting structure, or of conical bodies having a large apex angle,such that their planes of inflow include an acute angle with the centralaxis of the main shaft of the supporting structure, leads to anincreased mass flow passing the wind energy conversion apparatus, whichin turn leads to an increased energy output. All this can be traced backto the fact that the inclined position of the wind capturing meanscreates an underpressure near the main shaft, which leads to a certaincontraction of the oncoming wind. As will be explained in more detailyet in the description of the figures, all this leads to a significantincrease of the energy output that can be obtained from the oncomingair.

Another embodiment of the wind energy conversion apparatus according tothe invention is characterized in that each of the wind capturing meansconsists of a rotor having at least two rotor blades, wherein each rotoris mounted on a rotor shaft, which is rotatably journalled on the end ofan associated spoke in such a manner that the plane in which the rotorblades lie includes an acute angle with the central axis of the mainshaft and intersects said main shaft upstream, wherein the rotor shaftof each rotor is coupled with means, such as a generator, for convertingrotation energy into electric energy. Also in this embodiment of theapparatus according to the invention the aforesaid effect of contractionof the oncoming air flow will occur, resulting in an increased mass flowthrough the rotors and thus an increased energy output.

According to another embodiment of the apparatus according to theinvention the main shaft of the supporting structure includes means forrotating the same. Said means may consist of an electric motor, which iscapable of rotating the supporting structure. In this manner it is notthe wind velocity but the electric motor that determines the speed ofthe main rotor, thus enabling easy protection and control the apparatus.

In another embodiment of the apparatus according to the invention thewind capturing means are conical bodies having a large apex angle, whosebase is directed towards the oncoming wind, which conical bodies areconnected to the ends of their associated spokes in such a manner thatthe base of each conical body includes an acute angle with the centralaxis of the main shaft of the supporting structure, intersecting saidcentral axis upstream of the main shaft. Owing to the inclined positionof the bases of the conical bodies relative to the main shaft, an areaof lower pressure is created round the main shaft again, resulting in anincreased mass flow of the air that passes the conical bodies andconsequently in an increased energy output.

Another embodiment of the apparatus according to the invention ischaracterized in that a number of spokes of the supporting structurecarry a rotor and in that a number of spokes have a conical body mountedthereon.

According to the invention the acute angle that the aforesaid windcapturing means include with the central axis of the main shaft isadjustable between 80° and 10°, preferably between 60° and 30°.

The invention will be explained in more detail hereafter with referenceto the drawing.

FIGS. 1 and 2 are a schematic side view and a schematic front view,respectively, not to scale, of a wind energy conversion apparatuscomprising rotors which are mounted in an inclined position on asupporting structure.

FIG. 1a schematically shows the diverging portion of a well-knownventuri tube.

FIGS. 3 and 4 schematically show, not to scale, a wind energy conversionapparatus comprising conical bodies mounted in an inclined position onthe spokes of the supporting structure.

FIGS. 5 and 6 schematically show, not to scale, a wind energy conversionapparatus comprising a supporting structure including a number ofspokes, on which rotors and conical bodies are alternately mounted in aninclined position.

FIG. 7 schematically shows, not to scale, an alternative embodiment ofthe wind energy conversion apparatus according to the invention.

FIGS. 1 and 2 show a wind energy conversion apparatus comprising ahorizontally extending main shaft 1, which carries a supportingstructure comprising three spokes 2, on the end of which rotors 3 aremounted, each of which rotors is coupled with a generator 4.

Rotors 3 are mounted on spokes 2 in such a manner that the plane ofinflow 5 of said rotors includes an acute angle α with the central axisof the main shaft 1 and that said plane 5 intersects the central axis ofthe main shaft 1 at a point 6 located upstream, seen in the direction offlow 7 of the oncoming wind. The value of angle a thereby ranges between80° en 10°, more preferably between 60° and 30°. The main shaft 1 isfurthermore supporting in bearings at 10, in a structure 11 which issupported by a tower 12. Main shaft 10 is furthermore coupled to a anelectric motor 13, which is capable of rotating the main shaft 1 of thesupporting structure under certain circumstances. The oncoming wind 7will cause rotors 3 to rotate, with the wind reaction force 15 fromrotors 3 being perpendicular to plane 5. Said force can thereby beresolved into force 16, which acts parallel to the main shaft 1, and aforce 17, which acts in the radial plane of supporting structure 2. As aresult of said radial force 17, an underpressure will be generated inthe area 18 surrounding the main shaft, and said force 17 willfurthermore cause air to be transported in radially outward direction ata downstream location. Owing to the underpressure in area 18, the airflow will be contracted, as a result of which the mass flow through theentire apparatus and through the plane of rotors 3 will increase andmore energy can be extracted from the air flow. Said increase in theenergy extraction may run up to as much as 40 to 50 percent of theenergy that can be extracted with a rotor arrangement wherein the angleα is 90°. This simple measure thus constitutes a major improvement of awind energy apparatus.

The aforesaid effect of contraction of the oncoming air flow can becompared with that which occurs in the diverging portion of a venturitube. Said portion 19 is schematically shown in FIG. 1a by way ofillustration, whereby the figure furthermore indicates the manner inwhich an oncoming air flow 7′ is subjected to a constriction in thethroat 18′ of said venturi tube. This well-known effect causes the massflow through the venturi tube to increase strongly. Surprisingly, it hasbecome apparent that this well-known venturi effect also occurs in theapparatus according to FIGS. 1 and 2, wherein the inclined position ofthe rotors 3 creates a conical covered surface which acts more or lessas a venturi tube, as a result of which the aforesaid effect isobtained.

FIGS. 3 and 4 show a wind energy conversion apparatus wherein conicalbodies 20 having a large apex angle rather than rotors are mounted onthe spokes 2 of the supporting structure, wherein the base 21 of saidconical bodies is directed towards the oncoming wind, said plane ofinflow being so inclined as to include an angle α with the central axisof the main shaft 1, intersecting said main shaft upstream. Also in thisconstruction the wind reaction force 22 of the bases 21 can be resolvedinto a force 23 parallel to the main shaft and a force 24perpendicularly thereto, which acts in outward direction. As a result ofthis radially outward force 24 an underpressure will be created again inthe area 18 surrounding the main shaft. This will again lead tocontraction of the air flow, as a result of which the mass flow of theair that passes the apparatus will increase, and thus also the energy tobe extracted from said air flow. All this is again comparable with theventuri effect that occurs in the venturi tube that is shown in FIG. 1a.It will be understood that in addition to being inclined as mentionedabove, the cones will also need to be tilted slightly about the linethrough points 6 and 30, so that a force will be exerted on said cones,which force is in this case directly transmitted via spokes 2 to themain shaft 10, which operates a generator 26 that converts therotational energy into electric energy.

FIGS. 5 and 6 schematically show a further embodiment of the apparatusaccording to the invention, wherein rotors 3 and conical bodies 20 aredisposed in alternating relationship on the spokes 2 of the supportingstructure. The aforesaid effect of creating a certain underpressure inthe space surrounding main shaft 1 occurs in this case as well, whichagain leads to an increased mass flow and an increased conversion of thewind energy into rotational energy.

Also in this case the main shaft 1 is coupled to an electric motor 13,which provides protection and control. It will be understood that thenumber of rotors 3 and conical bodies 20 may be different from thenumber shown in the figure.

Although the preceding figures show embodiments wherein a supportingstructure 2 comprising rotos 3 or conical bodies 20 are shown to bedisposed on tower 12, it may be advantageous under certain circumstancesto mount on tower 12 a structure consisting of two supporting structures2 comprising spokes, which each carry rotors or conical bodies. Such astructure is schematically shown, not to scale, in FIG. 7.

It will be apparent from the foregoing that the invention provides awind energy conversion apparatus comprising wind capturing means (rotorsand conical bodies or a combination thereof), which are so inclined thatthey will move over the circumferential surface of a truncated cone uponrotation of the supporting structure, resulting in a venturi effect onthe air flow. It is important thereby that the inner side of thisfrustoconical surface forms a practically unimpeded passage for the windand has a dimension that provides the desired venturi effect. Thediameter of the truncated cone on the inflow side is thereby at leastsubstantially half as large as the diameter on the outflow side.

What is claimed is:
 1. A wind energy conversion apparatus comprising asupporting structure including a number of spokes (2), which isrotatably journalled on a horizontal main shaft (1), wherein windcapturing means (3) having an at least substantially circular plane (5)are mounted on the ends of said spokes, characterized in that each ofsaid wind capturing means has a plane (5) which includes an acute angle( ∝) with the central axis of the main shaft (1), such that the windcapturing means move over the circumferential surface of a truncatedcone upon rotation of the supporting structure, which acute angle ( ∝)intersects (6) said main shaft upstream and wherein the diameter of thetruncated cone on the inflow side is thereby at least substantially halfas large as the diameter on the outflow side.
 2. A wind energyconversion apparatus according to claim 1, characterized in that each ofthe wind capturing means consists of a rotor having at least two rotorblades (3), wherein each rotor is mounted on a rotor shaft, which isrotatably journalled on the end of an associated spoke (2) in such amanner that the plane (5) in which the rotor blades lie includes anacute angle ( ∝) with the central axis of the main shaft (1) andintersects (6) said main shaft upstream, wherein the rotor shaft of eachrotor is coupled with means (4), such as a generator, for convertingrotation energy into electric energy.
 3. A wind energy conversionapparatus according to claim 1, characterized in that said windcapturing means are conical bodies (20), whose base (21) is directedtowards the oncoming wind (7), which conical bodies are connected to theends of their associated spokes (2) in such a manner that the base ofeach conical body includes an acute angle ( ∝) with the central axis ofthe main shaft (1) of the supporting structure, intersecting (6) saidmain shaft upstream.
 4. A wind energy conversion apparatus according toclaim 1, characterized in that a number of spokes (2) of the supportingstructure carry a rotor (3) and in that a number of spokes have aconical body (20) mounted thereon.
 5. A wind energy conversion apparatusaccording to claim 1, characterized in that the main shaft (1) of thesupporting structure comprises means (26) for rotating the same.
 6. Awind energy conversion apparatus according to claim 1, characterized inthat the acute angle that the aforesaid wind capturing means includewith the central axis of the main shaft is adjustable between 80° and10°.